Spirit levels are old and well known and enjoy wide usage by artisans, such as, carpenters and masons, as well as by relatively unskilled laymen, such as, homeowners and hobbyists. In general, a spirit level comprises an elongated frame having at least one straight, planar surface and a vial or vials carried by the frame. The vial contains a liquid with an entrapped bubble. Typically, the planar surface is placed on or against a workpiece and, when the bubble is perfectly centered between the markings on the vial, that workpiece is known to be level or straight. Of course, the accuracy of the spirit level is dependent upon a precise geometric relationship between the axis of the vial and the straight surfaces of the frame, e.g., parallel or perpendicular thereto.
A matter of primary importance relating to spirit levels is the accurate mounting and retention on the frame of the liquid vial to achieve the precise geometric relationship required. Where cost is no object, such precision mounting can be achieved with expensive manufacturing techniques wherein notches, grooves and the like are made to close tolerances in the frame, and the level is permanently pre-assembled by the manufacturer.
However, the cost of a level is a major concern to the average purchaser and user of such devices. Moreover, most relatively inexpensive spirit levels are sold in knocked down form, that is, with the liquid vials separate and unmounted in the frame. Under those circumstances, the assembly of the level and accurate mounting of the liquid vial or vials on the frame can present difficult problems for the average person.
As an indication of the multitudinous efforts that have heretofore been made to supply the ideal spirit level, the following U.S. Pat. Nos. were located during a prior art search related to the subject invention: 650,751, 786,269, 876,720, 1,225,132, 1,233,756, 1,462,430, 1,777,429, 1,826,731, 2,502,235, 2,502,905, 2,576,202, 2,639,514, 2,646,628, 2,810,206, 2,948,066, 2,993,281, 3,167,870, 3,190,010, 3,311,990, 3,442,024, 3,456,354, 3,593,428, 3,738,015, 3,750,301, 3,793,735, 3,835,549, 3,869,806, 4,011,660, 4,124,940, 4,208,803, 4,335,524, and 4,407,075.
While all of the cited references deal with spirit levels, the disclosed designs can be characterized as exhibiting one or more of the problems inherent in such devices, such as, high cost, difficulty of assembly, precision mounting requirements, likelihood of misalignment during use, and the like, which render them unsuitable for sale in knocked down form to the average unskilled person. Typically, the mounting openings of the prior devices (except for that disclosed in U.S. Pat. No. 1,797,429) are circular, or some complex variation of circular, which makes difficult the accurate positioning of the vials.
There thus exists a need for a spirit level which is relatively inexpensive and has mounting means which are substantially foolproof so that the average person can readily assemble the level and accurately mount the vials thereon.